1. Field of the Invention
In general, thin film transistor liquid-crystal displays (TFT-LCD) employ RGB color-filters fabricated by black and R {grave over ( )} G {grave over ( )} B photosensitive resin, wherein the RGB color-filters exhibits high transparency and superior color saturation. Conventional pigments have high transparency and superior color saturation optical properties, but have poor thermal property and light stability.
In order to solve the aforementioned problems, a color photoresist prepared by a pigment modified and dispersing process have been developed and is widely used in full-color display fabrication.
Within the development of large-sized displays, the enhancement of display brightness has been studied continuously in last 10 years. Along with the monitor brightness promotion, the monitor operating temperature also relatively enhances. Therefore, the pigment stability is relatively important. Furthermore, reducing the pigment size is apt to improve the color saturation and contrast and reduce scattering of light.
Due to the high optical properties requirement of light transparency for color filters, the pigment size should be reduced to nano-dispersion. However, as pigment size reduces to nano scale, the surface area and surface energy will increase (according to the second law of thermodynamics). Additionally, pigment particles are apt to gather together when it reduced to nano scale. To stabilize the nano pigment, more dispersing agent is needed to decrease the surface tension. However, as the amount of dispersing agent used increased, and the viscosity of pigment composition will increase and then the compatibility of the photo resist will decrease.
The contrast of the color filter depends on the contrast enhancement of the photo resist. U.S. Pat. No. 20040235985 discloses an organic pigment packaged with high transparent polymer, enhancing the transparency and contrast of the color filter. Further, modified inorganic nano particles can serve as the core and the pigment is packaged to the core, resulting in high contrast of photo resist.
U.S. Pat. No. 6,100,312 discloses a graft copolymer serving as a dispersing agent to mix with a pigment for producing nano-dispersion under 60 nm. Moreover, U.S. Pat. No. 5,968,688 discloses a pigment packaged with transparent resin and modified by anthraquinone or phthalocyanine, in order to enhance thermal and color stability.
However, the previous invention improve the thermal property and stability of photo resist but the improvement of scattering and polarization effect which comes from the crystalline of pigment is not mentioned. In this patent, ours invention provides a method to prepare pigments with low crystallization degree, in order to reduce the effect of scattering and polarization and increase the contrast of a color filter.